Construction of Berrys Weir partial width rock ramp fishway on the Bremer River in Ipswich was completed in October 2016. The fishway was constructed on a large 2.4 m high barrier (Berrys Weir), making this the longest rock ramp fishway in Australia.
Berrys Weir on the Bremer River was constructed in the 1960’s to impound water for power generation, forming a major barrier to fish migration (Figure 2). The weir was constructed in the lower reaches of the Bremer River, impacting crucial life-cycle dependant migrations between downstream estuarine environments and upstream freshwater habitats. The barrier impacted many native species including a number of economically important fish species, such as Australian bass, sea mullet, and long-finned eels. The Bremer River is also home to the endangered Mary River Cod, which have been re-introduced as part of conservation efforts to save their population. Barriers to fish passage are widely known to adversely impact on fish populations, so the re-opening of over 41 kilometres of riverine habitat along the Bremer River is a big step in the right direction for the recovery of this endangered species.
Berrys Weir was highly ranked during a recent fish barrier prioritisation project conducted by Catchment Solutions (Moore, 2016 Greater Brisbane Fish Barrier Prioritisation). The fish barrier prioritisation was funded by the Australian Government’s Target Area funding stream. The sites’ close proximity to estuarine habitats (~3 kilometres), large area of blocked upstream habitat, and large height of the barrier contributed to its high priority ranking. Through this process Berrys Weir was ranked the seventh most important fish barrier in South-East Queensland. In collaboration with Ipswich City Council, Catchment Solutions set about remediating the lack of fish passage through the installation of a fishway.
A partial width rock ramp fishway was chosen as the most appropriate option to improve connectivity along the lower reaches of the Bremer River. Rock ramp fishways are excellent at facilitating fish passage for the whole fish community; including really small bodied fish and economically important juvenile diadromous fish species as well as adults. Rock ramp fishways are also inexpensive and have a natural appearance when compared to their highly engineered smooth sided vertical-slot fishway cousins.
The rock ramp fishway was funded by the Australian Government and Ipswich City Council, with in-kind assistance from Stanwell Power (asset owners).
The partial width rock ramp fishway extends 90 m in length in a zig-zag (dog leg) configuration, and consists of 33 ridges and pools (cells). The fishway was designed to operate at low and medium flows with a slope 1V:27H. Due to the proximity to estuarine habitats, falls (drops) between ridges and pools were set at 75 mm to cater for weaker swimming juvenile diadromous and small bodied species within the system (Figure 3). Fishway pools were approximately 2 -3 m² and ranged between 0.4 – 1 m in depth during low flows. This provided the resting areas and turbulence dissipation juvenile and small bodied species need to negotiate the large fishway. Ridges consisted of 3 slots, with each slot approximately 100- 250 mm wide and 200-400 mm high, allowing the fishway to operate over a range of flow conditions.
Construction of the fishway involved a 21 t excavator fitted with a hydraulic rock grab. The grab was used to place the 500 t of large igneous rock between 1 – 2.5 m and weighing up to 5 tonnes into specific positions to from the ridges and side walls. 32 m³ of fibre reinforced concrete was pumped into position to seal fishway pools and set fishway ridge controls to design levels. A 100 mm high concrete nib wall was constructed on top of the existing weir to divert low flows through the fishway.
In high flow situations when the fishway features drown out, the design provides a steady slope of 1V:14H from the weir crest to the downstream bed as well as the 1:27 slope of the low flow path. Although not sampled during high flows, there are reports of large adult fish (e.g. Australian bass and bullrout) migrating in SEQ streams during these conditions. It is not known whether these fish are able to negotiate the 1:14 overall slope, or track the 1:27 slope of the low flow path. However, given that the existing conditions at this site had an overall slope of 1V:9H with a 1 – 1.2 m vertical drop abutting the weir crest, it is anticipated that the fishway has greatly improved fish passage past the weir in high flows.
Fishway trap monitoring was successfully undertaken across five days in mid-December 2016. For the majority of the sampling period low flow conditions were present, on days four and five flows elevated to moderate as a result of local storm inflows. This provided an opportunity to observe fish movement over changing conditions.
Fishway monitoring results demonstrate that the fishway is operating successfully, with 3514 individual fish representing 21 species (19 native and 2 introduced species) sampled. A catch rate of 690.4 fish/day was recorded across the duration of monitoring. Significantly, native fish represented 99.94% of the catch, with only two alien fish representing two species (platy and tilapia) recorded. Hypseleotris species (unable to be positively identified in the field – specimens sent to the Qld Museum for correct identification which revealed both H. galii and H. klunzingeri) were the most abundant species representing 36.1% of the catch, followed by crimson-spotted rainbowfish, empire gudgeon, striped gudgeon and sea mullet with 25.7%, 16.5%, 11.6% and 5.7% respectively.
The smallest fish species recorded successfully ascending the fishway included a 15 mm Hypseleotris species, followed by crimson-spotted rainbowfish, empire gudgeon, flathead gudgeon and striped gudgeon (Figure 8) at 18 mm, 19 mm, 20 mm and 21 mm respectively. The largest fish species recorded included a 550 mm long-fin eel, followed by fork-tailed catfish (Figure 10), yellow-fin bream and bony bream at 350 mm, 254 mm and 254 mm respectively. The median size of all fish captured successfully migrating through the fishway equated to just 34 mm.
Diadromous species represented 32% of the total species captured, and 36% of total individuals. The smallest size diadromous species included; empire gudgeon 19 mm, striped gudgeon 21 mm, Australian bass 30 mm, bullrout 35 mm, sea mullet 38 mm, long-finned eel 70 mm and yellow-fin bream 254 mm (Figure 9). The median size of diadromous species included; empire gudgeon 35 mm, striped gudgeon 35 mm, Australian bass 35 mm, bullrout 54 mm, sea mullet 65 mm, long-finned eel 255 mm and yellow-fin bream 254 mm.
All fish species recorded successfully migrating through the fishway had to negotiate at least 1.5 m/sec through the ridge slot (low flow conditions), with many fish species migrating through minimum velocities up to 2.1 m/sec (moderate flow conditions).
Interestingly the median size of fish increased with the rise in river flow. During low flow conditions experienced between the afternoon of 15th December until mid-day on the 18th, the median size of fish moving through the fishway equated to 33 mm. A storm event on the afternoon of the 18th caused the river to rise rapidly, during this elevated flow period the median size of fish more than tripled to 110 mm. On the recession of this flow event (19th & 20th) smaller fish began to be more prevalent in captures with a median size of 55 mm. While only anecdotal, these results support the theory that larger fish move during elevated river flows, while juvenile and small bodied species migrate across all flow events, with a preference for low and receding flow conditions to undertake movement
For more information relating to the Berrys Weir fishway or other fishway projects underway in Queensland, please contact Catchment Solutions on (07) 4968 4216